1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly to an active matrix type liquid crystal display device.
2. Description of the Related Art
In recent years, performance of the liquid crystal display device has been increasingly improved, and thus there is a demand for products capable of performing WVGA display of 800×480 pixels even in small and medium-size liquid crystal display devices of 3 to 4 inches. However, in small and medium-size liquid crystal panels capable of performing the WVGA display, since plural display pixels (hereinafter, simply referred to as pixels) are required to be formed in a limited display region, the width of a single pixel width is about 30 μm. For this reason, there is a demand for further improvement in aperture ratio or improvement in display mode efficiency.
As a liquid crystal display device where the display mode efficiency is improved, there is a liquid crystal display device disclosed in, for example, JP 6-214244 A. In the liquid crystal display device disclosed in JP 6-214244 A, a pair of electrodes are formed at both ends of the pixel region, an image signal is supplied to one electrode (source electrode), and a common signal used as a reference is supplied to the other electrode (common electrode), thereby generating an electric field (a so-called horizontal electric field) parallel to the main surface of the liquid crystal display panel and driving liquid crystal molecules. Particularly, in the liquid crystal display device disclosed in JP 6-214244 A, the source electrode and the common electrode are formed in a wall shape so as to protrude toward the second substrate from the main surface of the first substrate, and the extending direction thereof is perpendicular to the main surface of the first substrate. With this configuration, in the liquid crystal display device disclosed in JP 6-214244 A, the density of the electric flux lines is the same from a region close to the first substrate to a distant region (a region close to the second substrate), and thereby display mode efficiency is improved.
On the other hand, in the small and medium-size liquid crystal display panels capable of performing the WVGA display, in order to improve the aperture ratio, the interval between the adjacent pixels becomes very small, and thus an interval between the source electrode of each pixel and the common electrode of the adjacent pixel also becomes very small. For this reason, in the liquid crystal display device disclosed in JP 6-214244 A, for example, in a region where a pixel performing white display and a pixel performing black display are adjacent to each other, the interval between the source electrode of the pixel performing white display and the common electrode of the adjacent pixel performing black display becomes very small. As a result, the electric flux lines generated from the source electrode of the pixel performing white display head toward the common electrode in the pixel and also head toward the source electrode of the adjacent pixel performing black display. In this case, the density of the electric flux lines between the source electrode and the common electrode in the pixel performing white display is high in the vicinity of the source electrode formed in a wall shape and the common electrode, and is low in a part distant from each electrode. That is to say, there is concern that the electric field intensity is non-uniform in the pixel region, and thus the display mode efficiency is reduced.
In addition, there is concern that electric flux lines heading toward the electrode of the pixel performing black display from the source electrode of the pixel performing white display are generated, the liquid crystal molecules in the pixel region performing black display are driven by the electric flux lines, thus the transmittance during the black display is increased, and thereby a dynamic range is lowered.
Further, signal lines such as a drain line may be considered to be formed under each electrode in order to improve the aperture ratio, but there is also concern that the liquid crystal molecules are driven by electric flux lines heading toward each of adjacent electrodes from each signal line, and thus the transmittance is increased during the black display.